1. Field
The present disclosure relates to a channel device such as a microchannel device capable of thermal analysis or the like, and a method for manufacturing the same.
2. Description of the Related Art
In order to obtain the course of biochemical reaction and the results of chemical analysis, various devices and sensors have been developed. As one of such devices, microdevices that have, in a substrate, a fine structure such as a channel having a predetermined shape or a microchannel have been proposed. These microdevices are downsized by using a semiconductor manufacturing method or the like, and all steps of an analysis process to obtain desired information can be performed on a microdevice. Such a device is called micro total analysis system (μ-TAS) or lab-on-a-chip. A structure having, in a substrate, a fine structure such as a microchannel is called microchannel device. Each part of a microchannel device has a size exemplified in embodiments and examples described later.
In the case of these microdevices, as compared to conventional desktop-sized analysis devices, the amount of fluid contained in the device is reduced, and reduction in the amount of reagent needed, and reduction in reaction time due to reduction in the amount of analyte are expected. For example, in the case of a microdevice such that a heater (resistor element) is disposed in a microchannel, and fluid passing through the microchannel is heated, the fluid capacity is small, and therefore the microdevice has good temperature following capability with respect to the heater, and the temperature can be rapidly increased and decreased. By using such a microdevice, for example, PCR (polymerase-chain-reaction) of DNA can be performed in a shorter time.
Many of such microchannel devices having a microchannel employ a glass substrate as a base. In general, glass substrates are bonded together in order to form a microchannel. For example, there is a bonding method such as a direct bonding method including forming a groove to form a microchannel in a glass substrate by etching, preparing a substrate serving as a cover on the opposite side, and applying pressure to the two substrates in a bonded state (see Japanese Patent No. 4348454). Such a bonding method does not affect the microchannel, but an accurate plane is required for bonding. In order to bond a large number of devices at the same time in view of mass production, the pressing force needs to be very large, a large apparatus is needed, and therefore manufacturing cost increases. So, a more inexpensive bonding method has been desired.
In the case of a microchannel device made of plastic and resin, bonding by heating, ultrasonic waves, laser light, organic adhesive, and the like can be used in the bonding step. However, in the case of press-bonding by heating, the resin substrate itself forming the device is deformed by heat, the shape of the microchannel changes, and it is not easy to reproduce the accurate shape of the microchannel. If the shape of the microchannel changes, the volume of solution caused to flow through the microchannel changes. Therefore, when a controlling method is used in which a fixed amount of fluid is caused to flow through a microchannel, and the position of the fluid is detected by fluorescence or the like of the fluid, the change in the shape of the microchannel is a problem. In the case of bonding by ultrasonic waves, bonding is possible when the size of the device is several millimeters square. However, when the size of the device is several tens of millimeters square or larger, the intensity distribution of ultrasonic waves is large, nonuniformity in bonding strength occurs, and it is not easy to obtain reproducibility and reliability of bonding. In the case of bonding by laser light, resin is required to have transmission for light of a wavelength of laser light. Depending on circumstances, laser light may be absorbed in a place other than the bonded surface, heat may be produced, and the place may be deformed. A laser light oscillating device is expensive, and a high cost is required for manufacturing.
So, a bonding method by organic adhesive is devised. A groove to form a microchannel is formed in a glass or resin substrate, and this substrate and a substrate serving as a cover are bonded with adhesive. In the case of bonding by adhesive, if the thickness of the adhesive layer is small, voids may be formed on the bonded surface owing to the minute unevenness of the substrate. If voids are formed, the bonding area decreases, therefore bonding force decreases, and separation is caused. If voids are formed close to microchannels, the microchannels may be connected by the voids, and solutions may be mixed. If the thickness of the adhesive layer is large, during bonding, surplus adhesive may fall into the groove forming the microchannel, and the microchannel may be filled with adhesive. If a substrate forming a microchannel and a substrate serving as a cover are bonded only with adhesive, owing to the change in thickness of the adhesive layer, the height of the cross-sectional shape of the microchannel may change along the extending direction of the channel.
There is a method in which, when bonding with adhesive, a soft film is used as a substrate serving as a cover to avoid the influence of minute unevenness, as in a method described in Japanese Patent Laid-Open No. 2008-175795. However, when a film is used, the dimension and shape of the microchannel may vary owing to the flexure or the like of the film. There also is a method in which a bank is provided around a microchannel so that adhesive does not flow into the microchannel, as in a method described in Japanese Patent Laid-Open No. 2007-21790. However, in a configuration in which a bank is provided around a microchannel, when a plurality of microchannels are arranged, it is difficult to reduce the intervals between the microchannels to close up the microchannels. It may be thereby made difficult to increase the density of microchannels to downsize the device. Bonding the bank by a method other than the method for bonding the substrates may complicate the manufacturing process and may increase the manufacturing cost.